EP 0 669 109 B1 discloses a stabilization apparatus for stabilizing neighboring thoracic vertebrae, which comprises two monoaxial pedicle screws and a strap that is fixed in the receiver members of each pedicle screw by means of a clamping screw and which contains a support element that is mounted on the strap and is designed as a pressure-resistant body. However, this stabilization apparatus fails to be torsionally stiff. In addition, the use of monoaxial pedicle screws limits the application of this stabilization apparatus. A similar stabilization apparatus where polyaxial pedicle screws are used instead of monoaxial pedicle screws is known from EP 1 188 416 A1.
A joint fixation apparatus, for example for a wrist or a knee joint, is disclosed in U.S. Pat. No. 6,162,223. The apparatus comprises a fixation rod that is connected to bone anchoring elements at its ends and consists of two parts, wherein the two parts of the fixation rod are connected to one another via a flexible coupling and wherein the fixation rods and the coupling are arranged outside of the body. The ends of the two parts of the fixation rod that are facing each other are designed hemispherically and abut against each other, thus simulating a type of joint whose freedom of movement is limited by the flexible coupling. Owing to its complex and voluminous structure, this known joint fixation apparatus is not suitable for being used on the spinal column.
US 2003/0109880 A1 discloses a dynamic stabilization apparatus for vertebrae, which comprises first and second screws to be anchored in the vertebra, with each screw being provided with a receiver member for insertion of a coil spring that connects the screws. The spring itself, as a whole, is designed in the form of a coil spring with closely adjacent windings, similar to a tension spring, and is fixed in the receiver members by means of clamping screws. This, however, poses the risk that the spring, owing to its flexibility, evades the pressure of the clamping screw, thus causing the fixation between the bone screw and the spring to loosen.
US 2003/0220643A1 discloses a stretchable element to be used in an apparatus for preventing full extension between upper and lower vertebral bodies. The stretchable element may be, for example, an elastic cord or a spring.
US 2003/0191470A1 discloses an implant device having a rod portion with a center section that flexes when the patient bends their spine. The flexible section can be a linear rod having a variable cross-sectional shape or a non-linear rod having a portion bent in a U-like shape to one side of the axis similar to expansion sections in pipes undergoing temperature changes.
There remains a need for compact implant devices that permit the stabilization and limited movement of vertebrae or bones that are to be connected to each other.